Expandable graphites expand by about 50 to more than 600 % by volume on heating to temperatures above about 150.degree. C. This expandability is based on the fact that foreign constituents are embedded between the lattice planes of the graphite and these cause widening of the lattice plane interstices when energy is supplied. These foreign constituents can be, for example, metallic groups, halogens, OH groups, acid radicals, SO.sub.x and/or NO.sub.x. Those expandable graphites which can be obtained by treatment of the graphite with sulphuric acids and nitric acids and/or other oxidising agents, for example hydrogen peroxide, are known in particular. SO.sub.x - or NO.sub.x -expandable graphites are also referred to, depending on whether it is a species which liberates more SO.sub.x or more NO.sub.x during thermal expansion.
If such expandable graphites are heated in powder form to temperatures above 200.degree. C. in partly filled, closed moulds, they expand and fill the mould to form mouldings of relatively low stability. In addition to their relatively low mechanical stability, mouldings produced in this manner also have the disadvantage that, because of the sensitivity of the graphite to oxidation, they can be used in the long term only at temperatures below about 450.degree. C.
These undesirable properties of the expandable graphite, lightweight mouldings can be improved considerably by additions of ammonium salts of acid metal phosphates, in particular ethanolamine salts of acid aluminium phosphates.
However, it has been found that mouldings produced in this way from expandable graphite containing sulphur release unpleasant odours at fresh cut and fracture points, which is undesirable in particular for use in closed rooms.